GIS AND REMOTE SENSING ASSESSMENTS OF HYDROLOGIC SYSTEMS RESPONSES TO EXCESSIVE DROUGHTS IN ARID LANDS

The length of time spans separating runoff generating rainy events in a specific location determines the significance of changes imposed on ephemeral drainage systems by aerobic variables. With the excessive droughts and elongated no-runoff time spans the drainage systems under go several changes imposed by exogenous variables. Those processes of a degenerative nature, include, but not limited to, bank wind corrosion and collapses, sand, dust bio-remains and other windblown materials accumulation in channel bottoms.

PRMS model is used for modeling of drainage basins. Homogeneous response units (HRU) are delineated using GIS and remotely sensed data for several drainage basins in central Saudi Arabia. The watersheds are conceptualized as a series of interconnected flow planes and channel segments. Water and sediment Surface runoff are simulated over the flow planes into the channel segments; channel flow of water is simulated through the watershed channel system.

Significant changes in suspended sediment concentrations, flood hydrograph shape, runoff generation and peaking time are noted in all drainage systems studied. The changes are more significant when following a longer dry span and are noticeable in the first runoff event in the season. No significant morphometric changes in the drainage systems were detected.